The present invention relates to rubber reinforced resins. More particularly, the present invention relates to rubber reinforced resins having improved weather resistance and physical characteristics. In one embodiment, the present invention relates to an improved rubber reinforced styrene acrylonitrile resin.
It is previously known in the art to prepare rubber modified resins wherein the rubber is a copolymer or terpolymer containing ethylene, propylene and optionally a copolymerizable diene monomer. Such rubbers are known as EPDM rubbers. In U.S. Pat. No. 3,489,821 a blend comprising an EPDM graft terpolymer and a hard matrix resin is disclosed. At Col. 7, line 31, the reference teaches that the graft copolymer resin blend may be mixed with other resins and/or rubbers.
In U.S. Pat. No. 3,576,910, there is disclosed an ABS polyblend comprising matrix and grafted rubbers wherein the grafted superstrate consists at least principally of a monovinylidene aromatic hydrocarbon and an unsaturated nitrile, i.e., styrene acrylonitrile copolymer. Suitable rubbers for use in the polyblend include diene rubbers, acrylate rubbers, polyisoprene rubbers and mixtures thereof.
U.S. Pat. No. 4,585,832 disclosed weather and impact resistant resins containing both a grafted acrylate rubber and a different grafted rubber. The second rubber could be either an EPDM rubber or a diene based rubber. Amounts of acrylate from 60 to 97% based on total grafted rubber weight were employed. Unfortunately these resins generally possess an inferior low temperature toughness as measured by -20.degree. F. Izod impact testing.
In U.S. Pat. No. 4,397,987 a similar polyblend comprising a nitrile rubber and an EPDM graft rubber is disclosed. In Table 9, Col. I, a blend of an ungrafted EPDM rubber and HYCAR 4041, an acrylate rubber, was prepared. However, the compatibility of the rubber blend was so poor that the blend could not be cured.
Previously known rubber reinforced resins comprising an EPDM graft copolymer elastomer have demonstrated good toughness as evidenced by high impact resistance at 25.degree. C. and good weather resistance, particularly resistance to ozone and radiation degradation. These resins, however, have demonstrated poor ductility, as shown by generally low elongations of from about 10 to 20 percent as measured by ASTM test D-638 at 0.2 inches/minute. Frequently, such resins are characterized by a "cheesy" or friable nature when flexed or drawn. This poor ductility in the resulting rubber reinforced weatherable polymer is believed to be a result of a low level of crosslinking inherent in the EPDM graft copolymer rubber. Whereas good weather resistance results from the use of EPDM copolymer rubbers due to the inherent chemical stability of such rubber, the same stability results in only a poor or limited ability to crosslink the EPDM rubber or graft with matrix polymer. While to some extent this problem may be alleviated by the use of greater amounts of initiator in the grafting processes or high temperature post treatment, such variations involve increased cost and ultimate contamination of the resin resulting in decreased weatherability, poor appearance or decreased notched Izod strength.
It would be desirable to provide an improved resin having good 25.degree. C. Izod impact strength and weather resistance without loss of ductility. It would further be desirable to provide an improved styrene acrylonitrile resin achieving good low temperature Izod impact strength and weather resistance as well as good ductility without deleterious affects on the grafting or crosslinking in the EPDM rubber.